This invention relates to a device for determining the size and charge of colloidal particles, and, in particular to a device for measuring the electrophoretic mobility of colloidal sols or suspensions of small particles in a liquid, such as blood, milk, paints, inks and slurries.
A device designed to determine the size distribution and the electric charge of the particles in a colloidal sol has many potential applications. The device is suitable for use in the paint industry for controlling the optical and flow properties of paints, since these quantities are sensitive to particle size and charge. Further, the device can be used to monitor the size of particles as the particles flow around a grinding circuit prior to sintering for forming a ceramic.
Although there are a number of commercial devices for determining the size and charge of particles on the market, these conventional devices employ optical techniques which are inoperative with concentrated, opaque suspensions that are usually encountered in industry. On the other hand, the instruments to be described herein are applicable to opaque suspensions, because the instruments determine particle size from the measurement of the electroacoustic effects, rather than light.
The instruments described herein determine size and charge of particles in accordance with the method described by Richard W. O'Brien in U.S. patent application Ser. No. 07/328,254 incorporated herein by reference (hereinafter referred to as "the O'Brien Method". In sum, the O'Brien Method determines the particle charge and size distribution of particles in suspensions of arbitrary concentration by applying at least one of an unsteady electrical field of at least two frequencies and an unsteady mechanical force of at least two different frequencies to the suspension to accelerate the particles. The resulting acoustic waves or electrical responses ("the electroacoustic effect") are measured at each application frequency. A quantity known as the "frequency dependent electrophoretic mobility" (.mu.) of the particles is determined from the measurements and the size and charge are calculated from the frequency dependent mobility, which will also be referred to here as the "dynamic mobility". The O'Brien Method for determining the size and charge of colloidal particle involves a quantity, referred to as the "frequency dependent electrophoretic mobility".
Prior to describing the O'Brien Method and the instruments suitable for use, the definition of the "dynamic mobility" should be described.